The reinforcement of epoxy by MWCNTs is done to obtain the required properties of composites. However, the homogeneousdispersion of MWCNTs in epoxy is a critical problem. Hence, an attempt is made to optimize the processing conditions fordispersing the MWCNTs in epoxy by solvent dispersion technique. The epoxy/MWCNTs mixture was prepared using threemethods: (1) magnetic stirring at 55∘C, (2) hot air oven process at 55∘C, and (3) vacuum oven process at room temperature.The nanocomposites having 0.1 and 0.2 wt.% of MWCNTs were prepared, for each method. The mechanical properties ofnanocomposites were studied as per ASTM-D695, and the thermal conductivity was measured using KD2 probe. It is observedthat the compressive strength, Young’s modulus, and thermal conductivity of 0.2 wt.% of MWCNTs prepared by vacuum ovenmethod were found to be enhanced by 39.4, 10.7, and 59.2%, respectively, compared to those of pure epoxy. Though the propertiesof nanocomposites were increased with MWCNTs’ concentration irrespective of the processing techniques, the vacuum-processedsample showed the most enhanced properties compared to any other method. It is concluded that a unique method for thedispersion of MWCNTs in epoxy is the solvent dispersion technique with vacuum drying process.
1. Introduction
The usage of nanoparticles as the reinforcement in a polymermatrix is increased enormously to achieve the required prop-erties of composites. Among all the fillers such as TiO
2, ZrO2,
and nanoclay, multiwalled carbon nanotubes (MWCNTs)were paid a lot of attention because of their attractivemechan-ical properties which were reported by Gojny et al. [1].Good aspect ratio of MWCNTs with the specific surfacearea of 1300m2/g helps in effective stress transfer from thematrix, which was studied by Yu et al. [2]. The desirableproperties of MWCNTs made them a candidate for rein-forcing the polymer matrix. Kim et al. [3] found that thehomogenous dispersion of the MWCNTs which gives goodinteraction between the matrix and the reinforcement mustbe ensured, in order to achieve the improved properties ofepoxy/MWCNTs nanocomposites. Starkova et al. [4] alsoevaluated the mechanical properties of the epoxy-basedcomposites.The enhancement of Young’smodulus of 0.1 wt.%composites was found to be 2% compared to that of pureepoxy. Mahfuz et al. [5] studied the influence of MWCNTs
in epoxy, and it was found that the mechanical and thermalproperties of the composites were increased. It was observedby He and Tjong [6] that the homogeneous dispersion ofreinforcement was confirmed with an increase of electricalconductivity of the composites. It is observed from theprevious studies that the dispersion of reinforcement is oneof themost important factors in deciding the enhancement ofmechanical, thermal, and electrical properties of composites.
Apart from the dispersion, the functionalization ofMWCNTs is also an important factor. The functionalizationof MWCNTs increased the stress transfer at the interfaceof the matrix and MWCNTs, and it also helped to reducethe concentration of substrate metallic particles present inthe MWCNTs. The attachment of amine group, carboxylgroup, and ozone-treated MWCNTs was studied in orderto ensure the homogeneous dispersion of the MWCNTs inmatrix byMa et al. [7]. Buang et al. [8] observed that the usageof acid-treated MWCNTs showed homogeneous dispersionand less defects on the side walls of MWCNTs comparedto other functionalization techniques. Theodore et al. [9]studied the effect of various functionalized MWCNTs in
2 Journal of Nanotechnology
Table 1: Different methods for MWCNTs reinforcement.
Sample MWCNTs wt.% Acetone + MWCNTs Epoxy + acetone Removal of acetone after mixingA-H 0.1 0.1 Tip sonication Bath sonication Hot air oven at 55∘CA-H 0.2 0.2 Tip sonication Bath sonication Hot air oven at 55∘CB-M 0.1 0.1 Tip sonication Bath sonication Magnetic stirring at 55∘CB-M 0.2 0.2 Tip sonication Bath sonication Magnetic stirring at 55∘CC-V 0.1 0.1 Tip sonication Bath sonication Vacuum oven at RTC-V 0.2 0.2 Tip sonication Bath sonication Vacuum oven at RT
terms of thermal andmechanical properties. It was concludedthat the attachment of –COOH group on the side walls ofMWCNTs confirmed the enhancement of flexural strengthand flexural modulus by 25.5 and 54.8%, respectively, forthe 1 wt.% of reinforcement. Yu et al. [10] evaluated that thefracture toughness of epoxy reinforced with 1 and 3wt.%of MWCNTs was found to be enhanced by 1.29 and 1.62times, respectively. Similarly, the fatigue life was found tobe enhanced by 9.3 and 10.5 times for the same MWCNTsconcentration. Rahman et al. [11] optimized the mechanicalproperties of the epoxy reinforced with E-glass and amino-functionalized MWCNTs. The strength, Young’s modulus,and strain at fracture of epoxy/E-glass/0.3 wt.% of MWCNTswere found to be enhanced by 37, 21, and 21%, respectively. It isobserved from the previous studies that the functionalizationof MWCNTs is very much essential in order to utilize thefullest potential of the reinforcement.
The thermal conductivity of the epoxy nanocompositeshaving 0.5 and 1 wt.% of silica-coated MWCNTs was foundto be enhanced by 51 and 67%, respectively, by Cui et al. [12].The interfacial bonding between epoxy and MWCNTs wasalso confirmed by the increase of thermal conductivity andbroadening of the glass transition temperature (Tg) in thestudy by Pillai and Ray [13]. The MWCNTs were aligned inthe epoxy resin to achieve the required properties by Parket al. [14], and the thermal conductivity of epoxy/MWCNTsnanocomposites at room temperature (RT) was observedto be 55W/mK, and the stretched MWCNTs-epoxy sheetshowed the value of 100W/mK, whereas the same for pureepoxy was found to be 0.11W/mK at RT.
Though different types of research works are going on inthe field of epoxy-based nanocomposites, the homogeneousdispersion of reinforcement is yet to be achieved, and theunique way for the dispersion of MWCNTs in epoxy remainsunfulfilled. Hence, an attempt is made to optimize theprocessing parameters in order to improve the mechanicaland thermal properties of nanocomposites.
2. Materials and Methods
2.1. Materials. The MWCNTs were purchased from M/sShenzhen Nanotech Port Co., Ltd., China. The specificationsof as-received MWCNTs are as follows: outer diameter<10 nm, length 5–15 𝜇m, purity 97%, ash content <3%, andspecific surface area −250 to 300m2/g. Epoxy resin andhardener were received fromM/s Endolite, India, Inc., havingthe density of 2.25 and 0.94 g/mL, respectively.
2.2. Chemical Treatment and Characterization of MWCNTs.The MWCNTs were functionalized using the acid treatmenttechnique as suggested by Esumi et al. [15], which is brieflydiscussed here. The MWCNTs were dispersed in nitric andsulfuric acid mixture having the volume ratio of 1 : 3 andheated at 140∘C in an oil bath with continuous mechanicalstirring for 30min. After the chemical treatment, MWCNTswere washed with distilled water until the pH value of thesupernatant reached around 7. Then, the MWCNTs weredried in a hot air oven at 100∘C. Thus, the chemically treatedMWCNTs were obtained. The functional groups attachedon the side walls of the MWCNTs were confirmed by theFourier transform infrared spectroscopy (FTIR) technique.The concentration and types of functional groups present ontheMWCNTs depend on the time of reflux and acid strength.Motchelaho et al. [16] reported that the peaks identified at1360, 1710, and 3403 cm−1 were confirmed to be COO–, C=O,and –OH bonds, respectively, in the chemically modifiedMWCNTs. Peaks at 1710 and 3453 cm−1 were attributedto acidic groups like carbonyl, phenol, and lactol. Peak at1576 cm−1 was assigned to C=C bond in MWCNTs. Thedefects in the MWCNTs after the chemical treatment werestudied by the laser micro-Raman with 488 nm blue laser,where the defects were observed to be negligible.
2.3. Preparation of Nanocomposites. The resin and hardenerhaving the weight ratio of 1 : 0.4 were hand-mixed using astirrer rod for 15min. and poured into the die having thedimension of 50mm length and 9mm diameter. Then, themold was allowed to cure at 26 ± 2∘C for 3 hrs, and, thus,the pure epoxy specimen was obtained. The nanocompositeshaving 0.1 and 0.2 wt.% of MWCNTs were prepared by threemethods, and their detailed specifications are given inTable 1.
The epoxy resin was dissolved in acetone using bathsonication for 30min., and the MWCNTs were dispersed inacetone using tip sonication for 30min. Both were mixedtogether and bath-sonicated for another 45 minutes. Later,the acetone was removed using three methods, namely, hotair oven at 55∘C (A), magnetic stirrer at 55∘C (B), and undervacuumat room temperature (C).Then, the epoxy-MWCNTsmixture was mixed with required quantity of hardener bythe hand mixing process for 15min. and poured into the die.Thus, the nanocomposites were prepared once the mold wascured.
2.4. Characterization of Test Samples. The compression testof the sample was carried out as per ASTM D695 [17] using
Journal of Nanotechnology 3
0 0.5 1 1.50
500
1000
1500
2000
2500
3000
3500
4000
A-H 0.1Epoxy
B-M 0.1
B-M 0.2
A-H 0.2C-V 0.1C-V 0.2
Load
(N)
Compression (mm)
Figure 1: Load versus compression of epoxy nanocomposites.
a servo controlled closed loop Instron 8101. The thermalconductivity of the sample was measured by a KD2 Prothermal properties analyzer using a dual-probe method. ANetzsch simultaneous thermal analyzer model STA 449 F3having the DSC resolution of <1 𝜇W and the microbalanceresolution of <1 𝜇g was used for calorimetric analysis of thetest samples from room temperature to 800∘Cat a heating rateof 10 K/min. The test samples were prepared from the curedspecimens weighing in the range of 5–10mg. The samplechamber and the furnace chamber were purged with Ar gasbefore starting the test at 20 and 60ml/min., respectively.In all cases, three specimens were tested, and the average ofthe results is reported. The homogeneous dispersion of theMWCNTs in epoxy was also confirmed by the same.
3. Results and Discussion
3.1. Mechanical Properties of EpoxyNanocomposites. The loadversus compression plots obtained for test samples processedby different methods are shown in Figure 1. It is observedthat the strength of nanocomposites prepared by magneticstirring and vacuum oven process was increased. However,it was found to be decreased for the sample preparedthrough hot air oven process compared to that of pureepoxy. It is also observed that the compressive strengthof the nanocomposites was found to be increased withconcentration of reinforcement irrespective of the processingtechnique followed.
The compressive strength (CS) and Young’s modulus(EM) of test samples against processing conditions are shownin Figures 2 and 3, respectively. It is observed from Figures 2and 3 that the CS and EMof epoxywere found to be increasedwith the reinforcement of MWCNTs. However, the CS andEM of A-H 0.1 were observed to be decreased by 11.4 and
05
10152025303540455055606570
Com
pres
sive s
treng
th (M
Pa)
A-H 0.1Epoxy
B-M 0.1
B-M 0.2
A-H 0.2C-V 0.1C-V 0.2
Figure 2: Compressive strength of nanocomposites.
0
500
1000
1500
2000
2500
3000
3500
Youn
g’s m
odul
us (M
Pa)
A-H 0.1Epoxy
B-M 0.1
B-M 0.2
A-H 0.2C-V 0.1C-V 0.2
Figure 3: Young’s modulus of the test samples.
11.8%, respectively, compared to those of pure epoxy. It isdue to the fact that the method of removal of acetone byhot air oven led to destroying the chemical bonding betweenthe MWCNTs and epoxy leading to decreased propertiesof nanocomposites. However, it was restricted when theMWCNTs’ concentration was increased. Amount of heatsupplied to evaporate the acetone was not sufficient enoughto destroy the chemical bonding between them at 0.2 wt.%MWCNTs, and, thus, it led to the reduction of CS andEM by only 0.8 and 3.3%, respectively. The sample B-M
4 Journal of Nanotechnology
0
20
40
60
80
100
120
140
160
180
Gla
ss tr
ansit
ion
tem
pera
ture
(∘C)
A-H 0.1Epoxy
B-M 0.1
B-M 0.2
A-H 0.2C-V 0.1C-V 0.2
Figure 4: Glass transition temperature of the test samples.
0.2 showed the increase of CS and EM of nanocompositesby 14.2 and 3%, respectively, compared to those of pureepoxy resin. The enhancement of mechanical properties isdue to the fact that the continuous stirring of the epoxy andMWCNTs in acetone reduced the debonding between themat the evaporation temperature of acetone, and it is expectedto ensure the homogeneous dispersion ofMWCNTs in epoxy.The sample C which used the vacuum oven for removing theacetone showed a significant enhancement in the mechanicalproperties compared to those of the samples A and B. Duringthe vacuum condition at room temperature, the solvent wasfully removed compared to the rest of the process. Theenhancement of CS and EM of the C-V 0.2 sample wasobserved to be 39.4 and 10.7%, respectively, compared topure epoxy. The observed enhancement of EM of epoxy with0.1 wt.% MWCNTs was 3.4%, whereas it was reported to beonly 2% for the same reinforcement condition by Starkovaet al. [4]. The enhancement of mechanical properties of thenanocomposites was due to homogeneous dispersion of rein-forcement and good interaction between the reinforcementand the matrix, which was also confirmed by Gojny andSchulte [18]. A strong physical network between MWCNTsand epoxy was confirmed by the shifting of glass transitiontemperature (Tg) of the nanocomposites, which is shownin Figure 4, leading to enhanced mechanical properties. TheTg of C-V 0.2 was observed to increase by 16.8% comparedto that of pure epoxy confirming the previous observations.Guadagno et al. [19] confirmed the interaction between epoxyand MWCNTs with an increase of Tg and the homogeneousdispersion of the MWCNTs in epoxy. Pillai and Ray [13]confirmed the interaction between epoxy andMWCNTswiththe broadening of Tg.
3.2.Thermal Conductivity and Stability of EpoxyNanocompos-ites. Figure 5 shows the thermal conductivity of epoxy and its
A-H 0.1Epoxy
B-M 0.1
B-M 0.2
A-H 0.2C-V 0.1C-V 0.2
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Ther
mal
cond
uctiv
ity (W
/mK)
Figure 5: Thermal conductivity of nanocomposites.
nanocomposites prepared by different processing conditions,It is observed that the thermal conductivity of the sampleA-H0.1 and A-H 0.2 was found to be 33.4% and 25%, respectively,lower than that of the pure epoxy, which is due to debondingbetween the reinforcement and the matrix. It is also observedthat the thermal conductivity of samples B andCwas found tobe increasedwith the reinforcement ofMWCNTs.The sampleC showed significant enhancement of thermal conductivitycompared to that of samples A and B. The enhancement ofthermal conductivity is due to homogeneous dispersion ofMWCNTs in epoxy resin and bonding between them. Theenhancement of thermal conductivity was found to be 59.2%for C-V 0.2 compared to pure epoxy. The thermal stability ofthe sample was measured by the thermogravimetric analysis(TGA), and it is confirmed that the thermal stability ofnanocomposites was improved significantly compared to thatof pure epoxy, and it is shown in Figure 6. Venkata Ramanaet al. [20] also observed the improved thermal stability ofepoxy/MWCNTs nanocomposites compared to that of pureepoxy.
4. Conclusions
It is concluded that the compressive strength and Young’smodulus of nanocomposites were found to be significantlyincreased for the specimens processed by vacuum dryingat room temperature compared to any other method. Animproved physical network between MWCNTs and epoxywas confirmed by the enhancement of thermal conductivityand the thermal stability. The Young modulus, compressivestrength, and thermal conductivity of the vacuum ovenprocessed sample at 0.2 wt.% of MWCNTs were found tobe increased by 10.7, 39.4, and 59.2%, respectively, compared
Journal of Nanotechnology 5
0 50 100 150 200 250 300 350 400 450 500 550 6000
25
50
75
100
Wei
ght o
f the
sam
ple (
%)
Temperature (∘C)
A-H 0.1Epoxy
B-M 0.1B-M 0.2
A-H 0.2C-V 0.1C-V 0.2
Figure 6: Thermal stability of nanocomposites.
to those of pure epoxy. Therefore, a unique method forthe preparation of epoxy/MWCNTs nanocomposites is thesolvent dispersion technique with vacuum drying process,where maximum enhancement of mechanical and thermalproperties, homogeneous, dispersion of reinforcement in thematrix, and good interfacial bonding were obtained.
Technical support given by the staff from the Material Sci-ence Lab, Central Instruments Facility, Strength of MaterialsLab, and Advanced Manufacturing Lab of IIT Guwahati ishighly acknowledged. Funding support given by DBT, India,through Project BT/233/NE/TBP/2011 is also acknowledged.
References
[1] F. H. Gojny, M. H. G. Wichmann, B. Fiedler, and K. Schulte,“Influence of different carbon nanotubes on the mechanicalproperties of epoxy matrix composites—a comparative study,”Composites Science and Technology, vol. 65, no. 15-16, pp. 2300–2313, 2005.
[2] M.-F. Yu, B. S. Files, S. Arepalli, and R. S. Ruoff, “Tensile loadingof ropes of single wall carbon nanotubes and their mechanicalproperties,” Physical Review Letters, vol. 84, no. 24, pp. 5552–5555, 2000.
[3] M. Kim, Y.-B. Park, O. I. Okoli, and C. Zhang, “Processing,characterization, and modeling of carbon nanotube-reinforced
multiscale composites,” Composites Science and Technology, vol.69, no. 3-4, pp. 335–342, 2009.
[4] O. Starkova, S. T. Buschhorn, E. Mannov, K. Schulte, and A.Aniskevich, “Creep and recovery of epoxy/MWCNTnanocom-posites,” Composites A, vol. 43, pp. 1212–1218, 2012.
[5] H. Mahfuz, S. Zainuddin, M. R. Parker, T. Al-Saadi, V. K.Rangari, and S. Jeelani, “Reinforcement of SC-15 epoxy withCNT/CNF under high magnetic field: an investigation ofmechanical and thermal response,” Journal of Materials Science,vol. 44, no. 4, pp. 1113–1120, 2009.
[6] L. He and S. C. Tjong, “Carbon nanotube/epoxy resin compos-ite: correlation between state of nanotube dispersion and Zenertunneling parameters,” Synthetic Metals, vol. 162, pp. 2277–2281,2012.
[7] P.-C. Ma, S.-Y. Mo, B.-Z. Tang, and J.-K. Kim, “Dispersion,interfacial interaction and re-agglomeration of functionalizedcarbon nanotubes in epoxy composites,” Carbon, vol. 48, no. 6,pp. 1824–1834, 2010.
[8] N. A. Buang, F. Fadil, Z. A. Majid, and S. Shahir, “Characteristicof mild acid functionalized multiwalled carbon nanotubestowards high dispersion with low structural defects,” DigestJournal of Nanomaterials and Biostructures, vol. 7, no. 1, pp. 33–39, 2012.
[9] M.Theodore, M. Hosur, J. Thomas, and S. Jeelani, “Influence offunctionalization on properties of MWCNT-epoxy nanocom-posites,”Materials Science and Engineering A, vol. 528, no. 3, pp.1192–1200, 2011.
[10] N. Yu, Z. H. Zhang, and S. Y. He, “Fracture toughness andfatigue life of MWCNT/epoxy composites,” Materials Scienceand Engineering A, vol. 494, no. 1-2, pp. 380–384, 2008.
[11] M. M. Rahman, S. Zainuddin, M. V. Hosur et al., “Improve-ments in mechanical and thermo-mechanical properties of e-glass/epoxy composites using amino functionalizedMWCNTs,”Composite Structures, vol. 94, pp. 2397–2406, 2012.
[12] W. Cui, F. Du, J. Zhao et al., “Improving thermal conductivitywhile retaining high electrical resistivity of epoxy compositesby incorporating silica-coated multi-walled carbon nanotubes,”Carbon, vol. 49, no. 2, pp. 495–500, 2011.
[13] S. K. Pillai and S. S. Ray, “Epoxy-based carbon nanotubes rein-forced composites in advances,” in Nanocomposites—Synthesis,Characterization and Industrial Applications, B. Reddy, Ed., pp.727–792, 2011.
[14] J. G. Park, Q. Cheng, J. Lu et al., “Thermal conductivity ofMWCNT/epoxy composites: the effects of length, alignmentand functionalization,” Carbon, vol. 50, no. 6, pp. 2083–2090,2012.
[15] K. Esumi, M. Ishigami, A. Nakajima, K. Sawada, and H. Honda,“Chemical treatment of carbon nanotubes,” Carbon, vol. 34, no.2, pp. 279–281, 1996.
[16] M. A.M.Motchelaho, H. Xiong, M.Moyo, L. L. Jewell, and N. J.Coville, “Effect of acid treatment on the surface of multiwalledcarbon nanotubes prepared from Fe-Co supported on CaCO
3
:correlation with Fischer-Tropsch catalyst activity,” Journal ofMolecular Catalysis A: Chemical, vol. 335, no. 1-2, pp. 189–198,2011.
[17] ASTM D 695-10., “Standard Test Method for CompressiveProperties of Rigid Plastics,” 2010.
[18] F. H. Gojny and K. Schulte, “Functionalisation effect on thethermo-mechanical behaviour of multi-wall carbon nanotube/epoxy-composites,” Composites Science and Technology, vol. 64,no. 15, pp. 2303–2308, 2004.
6 Journal of Nanotechnology
[19] L. Guadagno, L. Vertuccio, A. Sorrentino et al., “Mechanical andbarrier properties of epoxy resin filledwithmulti-walled carbonnanotubes,” Carbon, vol. 47, no. 10, pp. 2419–2430, 2009.
[20] G. Venkata Ramana, B. Padya, R. Naresh Kumar, K. P. V.Prabhakar, and P. K. Jain, “Mechanical properties of multi-walled carbon nanotubes reinforced polymer nanocomposites,”Indian Journal of Engineering and Materials Sciences, vol. 17, no.5, pp. 331–337, 2010.
![s 1Lanter C!&ffsbore, ]Jnt.](https://static.documents.pub/doc/80x56/61ee5f460ac9e13f1e2fa5da/s-1lanter-campffsbore-jnt.jpg)
![Introduction to Nanotechnology What is Nanotechnology While many definitions for nanotechnology exist, the [National Nanotechnology Initiative] NNI calls.](https://static.documents.pub/doc/80x56/56649d9e5503460f94a88dbf/introduction-to-nanotechnology-what-is-nanotechnology-while-many-definitions.jpg)
